The legislation is The Work Health and Safety Act 2011 and specifically a workplace is defined in Section 8.
Referring to the Work Safe website, it says WHS legislation concerns a business or employer. Whilst the ATO considers strata to be an enterprise , strata schemes are not a business.
Therefore the WHS legislation does not apply (unless the strata employs directly say a concierge or an on site building manager and then the workplace is considered to be their office and not the whole building)
And the reason that any tradie on site should have their own insurance is that the strata is not their employer. The tradie is independent or employed by a larger business. The tradie (as sole trader) or the business then is responsible for the WHS needs of the worker. (as well as being responsible for any damage they cause or other event that the strata suffers a loss. But thats another topic)
As a final discussion point, if every location where (say ) a tradie worked was considered a workplace, then every footpath, road, park, etc etc would be a workplace and the respective owner would have to provide a “safe” workplace. That is not the case because the footpath or park is not a place of business.